1. Field
The present application relates to gas turbines, more particularly to an abradable turbine component, and a method to create an abradable mesh structure on a turbine component.
2. Description of the Related Art
In the gas turbine engine industry, there is an increasing drive towards producing gas turbines with higher efficiencies. In order to achieve these higher efficiencies, gas turbines are operating at increasingly higher turbine temperatures. An additional measure taken to achieving higher gas turbine efficiency, could be to keep a tight clearance between the turbine blade tips and the opposing surface. Ideally, the clearance, or gap, between the rotating turbine blades and the opposite turbine component would be small enough to minimize the air flow leakage between the pressure side of the blade and the suction side of the blade while still maintaining enough distance to account for manufacturing variances of the opposing component surfaces and the thermal growth of the components due to the high temperatures.
In order to cope with the extremely high temperatures within the flow path of the gas turbine, many turbine components that are within the fluid flow path require the use of thermal barrier coatings (TBCs) to protect the underlying components from the harsh environment in the fluid flow path. Coatings comprised of a ceramic structure that can withstand extreme temperatures and also have good abradability so that they can wear or abrade as necessary are often used on these turbine components. For example, the turbine ring segment which is located radially outwards of the turbine blade tips, may come into contact with the turbine blade tips during engine operation. Because of this turbine blade tip incursion into the coating on the ring segment surface, it is crucial that the coating has good abradability as it is highly undesirable for the expensive material of blade tips to wear and/or to increase the gap between the blade tip and the ring segment surface. An abradable, sacrifical surface on the turbine component opposite the blade tip provides a compromise so that a small minimal gap may be maintained while taking into account that because of transient thermal growth/distortion and manufacturing variances of the components, the blade tip may rub into the abradable coating causing the abradable coating to wear instead of the blade tips.
Typically, the abradable surfaces have been applied to the turbine component using a ‘subtractive’ method. The abradable coating comprising a porous ceramic material is applied and then subtractively removed with a water jet machining method, for example, to produce the desired abradable surface profile. However, subtractive methods used to produce the abradable surface profile on the turbine component add a significant cost to manufacturing the component. Directly adding the desired surface profile to the turbine component would be more cost effective.
Additive Manufacturing, or 3-D printing, has recently been successfully used to ‘print’ or manufacture components directly layer by layer. This manufacturing technology enables the optimization of the component design. In the case of an abradable surface, additive manufacturing enables the ability to produce the abradable surface with a more complex geometry while keeping the manufacturing cost down. Laser Powder Forming is an additive manuafacturing method which builds up metallic or ceramic parts directly using CAD data by melting a fine powder with a laser beam, layer by layer.